Method for fabricating semiconductor device

ABSTRACT

A method for fabricating semiconductor device includes the steps of: forming fin-shaped structures on a substrate; using isopropyl alcohol (IPA) to perform a rinse process; performing a baking process; and forming a gate oxide layer on the fin-shaped structures. Preferably, a duration of the rinse process is between 15 seconds to 60 seconds, a temperature of the baking process is between 50° C. to 100° C., and a duration of the baking process is between 5 seconds to 120 seconds.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly, to a method of conducting a rinse process afterforming fin-shaped structures.

2. Description of the Prior Art

With the trend in the industry being towards scaling down the size ofthe metal oxide semiconductor transistors (MOS), three-dimensional ornon-planar transistor technology, such as fin field effect transistortechnology (FinFET) has been developed to replace planar MOStransistors. Since the three-dimensional structure of a FinFET increasesthe overlapping area between the gate and the fin-shaped structure ofthe silicon substrate, the channel region can therefore be moreeffectively controlled. This way, the drain-induced barrier lowering(DIBL) effect and the short channel effect are reduced. The channelregion is also longer for an equivalent gate length, thus the currentbetween the source and the drain is increased. In addition, thethreshold voltage of the fin FET can be controlled by adjusting the workfunction of the gate.

However, the design of fin-shaped structure in current FinFETfabrication still resides numerous bottlenecks which induces currentleakage of the device and affects overall performance of the device.Hence, how to improve the current FinFET fabrication and structure hasbecome an important task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: formingfin-shaped structures on a substrate; using isopropyl alcohol (IPA) toperform a rinse process; performing a baking process; and forming a gateoxide layer on the fin-shaped structures. Preferably, a duration of therinse process is between 15 seconds to 60 seconds, a temperature of thebaking process is between 50° C. to 100° C., and a duration of thebaking process is between 5 seconds to 120 seconds.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow chart for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

FIG. 2 illustrates a top view for fabricating the semiconductor deviceaccording to an embodiment of the present invention.

FIGS. 3-4 illustrate cross-section views for fabricating thesemiconductor device along the sectional line AA′ shown in FIG. 2.

FIG. 5 illustrates a top view for fabricating the semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-5, FIG. 1 illustrates a flow chart for fabricatinga semiconductor device according to an embodiment of the presentinvention and FIGS. 2-5 illustrate a method for fabricating thesemiconductor device according to an embodiment of the presentinvention, in which FIG. 2 and FIG. 5 illustrate top views forfabricating the semiconductor device while FIGS. 3-4 illustratecross-section views for fabricating the semiconductor device along thesectional line AA′ shown in FIG. 2. As shown in FIGS. 1-3, a substrate12 such as a silicon substrate or silicon-on-insulator (SOI) substrateis provided, and fin-shaped structures 14 are formed on the substrate 12according to step 101. Preferably, the fin-shaped structures 14 formedat this stage include a ring-shape if viewed from a top view perspectiveas shown in FIG. 2. Moreover, if viewed from a cross-section perspectiveas shown in FIG. 3, the angles between the fin-shaped structures 14 andthe top surface of the substrate 12 are preferably right angles made ofplanar or straight lines at this stage, or more specifically the anglesincluded by the top surface of the substrate 12 and sidewalls of thefin-shaped structures 14 are made of planar or non-curvy vertical andplanar horizontal surfaces having no curvatures.

In addition, the fin-shaped structures 14 of this embodiment arepreferably obtained by a sidewall image transfer (SIT) process. Forinstance, a layout pattern is first input into a computer system and ismodified through suitable calculation. The modified layout is thendefined in a mask and further transferred to a layer of sacrificiallayer on a substrate through a photolithographic and an etching process.In this way, several sacrificial layers distributed with a same spacingand of a same width are formed on a substrate. Each of the sacrificiallayers may be stripe-shaped. Subsequently, a deposition process and anetching process are carried out such that spacers are formed on thesidewalls of the patterned sacrificial layers. In a next step,sacrificial layers can be removed completely by performing an etchingprocess. Through the etching process, the pattern defined by the spacerscan be transferred into the underneath substrate. In this embodiment, itwould be desirable to repeat the aforementioned SIT process oftransferring patterns to the substrate at least two times or more andsuch approach typically referred to as self-align double patterning(SADP) would form at least a ring-shaped structure on the substrate.

Alternatively, the fin-shaped structures 14 of this embodiment couldalso be obtained by first forming a patterned mask (not shown) on thesubstrate, 12, and through an etching process, the pattern of thepatterned mask is transferred to the substrate 12 to form the fin-shapedstructure. Moreover, the formation of the fin-shaped structures 14 couldalso be accomplished by first forming a patterned hard mask (not shown)on the substrate 12, and a semiconductor layer composed of silicongermanium is grown from the substrate 12 through exposed patterned hardmask via selective epitaxial growth process to form the correspondingfin-shaped structures 14. These approaches for forming the fin-shapedstructures 14 are all within the scope of the present invention.

After the fin-shaped structures 14 are formed, a flush process isconducted by using carbon tetrafluoride (CF₄) to remove polymers onsurface of the fin-shaped structures 14 according to step 102, and thena plasma treatment process is conducted to form an oxide layer on abottom surface of the fin-shaped structures 14 near the surface of thesubstrate 12 according to step 103. Specifically, the plasma treatmentprocess conducted at this stage preferably injects oxygen gas to thebottom portion of the fin-shaped structures 14, in particular theincluded angles between the fin-shaped structures 14 and the substrate12 to form an oxide layer made of silicon oxide. According to apreferred embodiment of the present invention, the formation of theoxide layer could facilitate the angles included by the fin-shapedstructures 14 and the substrate 12 to alter from angles made of planarsurfaces to angles made of curves or curved surfaces in the laterprocess, which could then be used to prevent fin-shaped structures 14from falling down as a result of reduced pitch size.

In this embodiment, the temperature of the plasma treatment processconducted to form the aforementioned oxide layer is between 135° C. to165° C. or more specifically at around 150° C., the pressure of theplasma treatment process is between 0.9 Torr to 1.1 Torr or morepreferably at around 1 Torr, and the duration of the plasma treatmentprocess is between 2.7 minutes to 3.3 minutes or more preferably ataround 3 minutes.

Next, a first cleaning process is conducted to remove the oxide layerremained on the surface of the fin-shaped structures 14 according tostep 104. Specifically, as shown in FIG. 4, the first cleaning processconducted at this stage preferably removes the oxide layer formed duringthe step 103, transforms the angles included between sidewalls of thefin-shaped structures 14 and the top surface of the substrate 12 fromangles made of planar surfaces to angles made of curved surfaces, and atthe same time removes majority of impurities remained on the surface ofthe substrate 12 and/or fin-shaped structures 14. In this embodiment,the cleaning agent used in the first cleaning process preferablyincludes but not limited to for example diluted hydrofluoric acid (dHF).

Next, a second cleaning process is conducted according to step 105 toremove polymers remained on surface of the fin-shaped structures. Inthis embodiment, the cleaning agent used in the second cleaning processpreferably includes but not limited to for example ozone (O₃).

Next, a third cleaning process is conducted according to step 106 toremove particles remained on the surface of the fin-shaped structures.In this embodiment, the cleaning agent used in the third cleaningprocess preferably includes but not limited to for example StandardClean 1 (SC1).

Next, a rinse process is conducted according to step 107 by usingisopropyl alcohol (IPA) to clean the surface of the fin-shapedstructures 14 and substrate 12, and a baking process is conductedimmediately afterwards according to step 108 to dry the fin-shapedstructures 14. It should be noted that in conventional art, a spin dryprocess is often conducted to dry the fin-shaped structures 14 after theaforementioned third cleaning process of using SC1 to clean thefin-shaped structures 14 is completed. Nevertheless, the approach ofcombining SC1 along with spin dry process typically induces higherviscosity and causes the fin-shaped structures 14 to fall down. Toimprove this drawback the present invention first uses isopropyl alcoholto clean the fin-shaped structures 14 and then conducts a baking processto dry the fin-shaped structures 14 thereafter. Since this approachcould dry the fin-shaped structures 14 under low viscosity environmentit would be desirable to prevent fin-shaped structures 14 from fallingdown.

In this embodiment, the temperature of the rinse process is preferablyat around room temperature, the duration of the rinse process is between15 seconds to 60 seconds, the temperature of the baking process isbetween 50° C. to 100° C., and the duration of the baking process isbetween 5 seconds to 120 seconds.

Next, an in-situ steam generation (ISSG) process is conducted accordingto step 109 to form a gate oxide layer on the fin-shaped structures 14.It should be noted that the fin-shaped structures at this stage stillprevent a ring-shaped overview if viewed from the top. Next, as shown inFIG. 5, a fin cut process could be conducted to separate the ring-shapedfin-shaped structures 14 into a plurality of rectangular fin-shapedstructures. It should further be noted that even though only a singlering-shaped fin-shaped structure is separated into two independentrectangular fin-shaped structures in this embodiment, according to otherembodiments of the present invention, it would also be desirable toadjust the quantity of fin-shaped structures depending on the demand ofthe product. Next, typical process used to form standard MOS transistorscould be conducted by forming shallow trench isolation (STI) around thefin-shaped structures, forming gate structures on and across thefin-shaped structures, forming spacers around the gate structures, andforming source/drain regions adjacent to two sides of the gatestructures. This completes the fabrication of semiconductor deviceaccording to an embodiment of the present invention.

Overall, since current fin-shaped structures fabricated throughaforementioned self-align double patterning (SADP) process typicallyinvolves going through a series of cleaning process, reduces the pitchesof the fin-shaped structures, and ultimately causes the fin-shapedstructures to fall, the present invention preferably introduces twoapproaches into the cleaning process to improve this issue.

First, the present invention uses CF₄ to remove polymers on the surfaceof the fin-shaped structures and then conducts an O₂ plasma process toform an oxide layer on the bottom of the fin-shaped structures as wellas the corners included by the fin-shaped structures 14 and thesubstrate 12. By doing so the first cleaning process conductedthereafter would be able to remove the oxide layer and alter the anglesincluded by the fin-shaped structure 14 and the substrate 12 from anglesmade by planar surfaces to angles having curved surfaces. Moreover thepresent invention uses isopropyl alcohol (IPA) to rinse the fin-shapedstructures after the aforementioned first cleaning process, secondcleaning process, and third cleaning process were completed, conducts abaking process to dry the fin-shaped structures, and then conducts a fincut process to separate the ring-shaped fin-shaped structure into aplurality of rectangular fin-shaped structures. By inserting the abovetwo approaches into a series of cleaning processes conducted in currentfin-shaped structure fabrication process, the present invention is ableto prevent fin-shaped structure from falling down as pitch reduces.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating semiconductor device,comprising: forming fin-shaped structures on a substrate; usingisopropyl alcohol (IPA) to perform a rinse process; performing a bakingprocess; and forming a gate oxide layer on the fin-shaped structures. 2.The method of claim 1, further comprising: performing a plasma treatmentprocess to form an oxide layer on a bottom surface between thefin-shaped structures; performing a first cleaning process to remove theoxide layer; performing a second cleaning process to remove polymers;and performing a third cleaning process to remove particles.
 3. Themethod of claim 2, further comprising using oxygen gas (O₂) to performthe plasma treatment process.
 4. The method of claim 3, wherein atemperature of the plasma treatment process is between 135° C. to 165°C.
 5. The method of claim 3, wherein a pressure of the plasma treatmentprocess is between 0.9 Torr to 1.1 Torr.
 6. The method of claim 3,wherein a duration of the plasma treatment process is between 2.7minutes to 3.3 minutes.
 7. The method of claim 2, further comprisingusing diluted hydrofluoric acid (dHF) to perform the first cleaningprocess.
 8. The method of claim 2, further comprising using ozone (O₃)to perform the second cleaning process.
 9. The method of claim 2,further comprising using Standard Clean 1 (SC1) to perform the thirdcleaning process.
 10. The method of claim 1, wherein a duration of therinse process is between 15 seconds to 60 seconds.
 11. The method ofclaim 1, wherein a temperature of the baking process is between 50° C.to 100° C.
 12. The method of claim 1, wherein a duration of the bakingprocess is between 5 seconds to 120 seconds.
 13. The method of claim 1,further comprising performing an in-situ steam generation (ISSG) processto form the gate oxide layer.
 14. The method of claim 1, wherein thefin-shaped structure comprises a ring-shaped fin-shaped structure, andthe method further comprises performing a fin cut process to cut thering-shaped fin-shaped structure after forming the gate oxide layer.